Sheet stacking apparatus, image forming system, and conveyance control method

ABSTRACT

A sheet stacking apparatus includes: a sheet stacker capable of stacking a sheet; a sheet conveyer that conveys the sheet to the sheet stacker; an openable member that can be opened/closed at time of taking out the sheet stacked on the sheet stacker; and a hardware processor that controls the sheet conveyer so as to convey the sheet to the sheet stacker in a case where an opened/closed state of the openable member is an intermediate state between a fully-opened state and a fully-closed state.

The entire disclosure of Japanese patent Application No. 2019-137842, filed on Jul. 26, 2019, is incorporated herein by reference in its entirety.

BACKGROUND Technological Field

The present invention relates to a sheet stacking apparatus, an image forming system, and a conveyance control method.

Description of the Related Art

Generally, an image forming apparatus (a printer, a copier, a facsimile, or the like) utilizing an electrophotographic process technology forms an electrostatic latent image by irradiating (exposing) a charged photosensitive drum (image carrier) with laser light based on image data. Then, toner is supplied from a developing device to the photosensitive drum on which the electrostatic latent image is formed, thereby visualizing the electrostatic latent image to form a toner image. Furthermore, after the toner image is directly or indirectly transferred to a sheet, the toner image is fixed at a fixing nip by being heated and pressurized, thereby forming the toner image on the sheet.

At this time, in a case where a sheet stacking apparatus is arranged (joined and connected) on a downstream side of the image forming apparatus, the sheet having the toner image formed thereon (hereinafter, also referred to as a “printed sheet”) is ejected from a sheet ejector of the image forming apparatus and stacked on a tray inside the sheet stacking apparatus. Generally, a sheet stacking apparatus has a function of stacking and storing a printed sheet in a tray (for example, see JP 2008-94584 A). Additionally, it is known that the sheet stacking apparatus has a configuration in which a large number of sheets are stacked while keeping a constant maximum height position of the stacked sheets by moving up and down a sheet stacker such as a tray according to a sheet stacking amount.

Meanwhile, many conventional sheet stacking apparatuses adopt a system in which sheets are stacked on a tray installed on an arm while the arm that supports the tray is installed below a sheet ejection port of the own apparatus. In such a sheet stacking apparatus, when the sheets are carried out to the outside of the apparatus, a door of the sheet stacking apparatus is opened by an arm attached to a cart (carrier) such as a trolley, and the carrier is inserted into the apparatus to receive and carry out the stacked sheets and the tray all together.

On the other hand, in such a conventional sheet stacking apparatus, the tray and the sheets stacked thereon are delivered all together to trolley and then transported. Therefore, a productivity problem has been pointed out because a sheet ejected from the image forming apparatus cannot be received (stacked) until the sheets on the tray are removed and the tray is reset inside the apparatus.

To solve the above-described problem, it is conceivable to provide the sheet stacking apparatus with: a configuration (such as a first tray) that temporarily stacks sheets ejected from the image forming apparatus; and a configuration (such as a second tray) to which the temporarily-stacked sheets are moved in order to carry out these sheets by the carrier or the like. With such configurations, a stacking process and a conveying process can be handled separately (independently), and therefore, improvement in productivity can be expected.

On the other hand, even in the case of having the above-described configurations, when the door is opened/closed in the conveying process, a safety device is required to be actuated to stop the apparatus in order to ensure safety of operator's work. Here, in the case where the apparatus is stopped, the productivity cannot be improved in the conveying process. Therefore, there is a trade-off problem between securing safety of an operator and improvement in the productivity.

SUMMARY

An object of the present invention is to provide a sheet stacking apparatus, an image forming system, and a conveyance control method, in which productivity can be improved while securing safety of an operator.

To achieve the abovementioned object, according to an aspect of the present invention, a sheet stacking apparatus reflecting one aspect of the present invention comprises: a sheet stacker capable of stacking a sheet; a sheet conveyer that conveys the sheet to the sheet stacker; an openable member that can be opened/closed at time of taking out the sheet stacked on the sheet stacker; and a hardware processor that controls the sheet conveyer so as to convey the sheet to the sheet stacker in a case where an opened/closed state of the openable member is an intermediate state between a fully-opened state and a fully-closed state.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention:

FIG. 1 is a view schematically illustrating an entire configuration of an image forming system according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating main blocks of a control system of the image forming system according to the present embodiment;

FIG. 3 is a diagram schematically illustrating a main part of a sheet stacking apparatus from a left side (downstream side in a sheet conveyance direction) of FIG. 1;

FIGS. 4A and 4B are diagrams illustrating operation of moving a sheet bundle stacked on a first tray to a second tray in the sheet stacking apparatus;

FIGS. 5A and 5B are diagrams illustrating operation after moving the sheet bundle to the second tray in the sheet stacking apparatus;

FIGS. 6A and 6B are diagrams illustrating operation in the sheet stacking apparatus after pulling out the second tray or the like on which the sheet bundle is placed;

FIGS. 7A and 7B are diagrams to describe work of carrying out the sheet bundle stacked on the second stacking tray, and work subsequent thereto in the sheet stacking apparatus; and

FIGS. 8A and 8B are diagrams to describe work and the like at the time of returning the second tray or the like to the sheet stacking apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. FIG. 1 is a view schematically illustrating an entire configuration of an image forming system 1 according to the present embodiment. FIG. 2 is a diagram illustrating main blocks of an entire control system included in the image forming system 1 according to the present embodiment.

As illustrated in FIG. 1, the image forming system 1 includes an image forming apparatus 2 and a sheet stacking apparatus 3 in the order from an upstream side along a conveyance direction of a sheet S. In the present embodiment, the image forming apparatus 2 and the sheet stacking apparatus 3 are connected in-line.

The image forming apparatus 2 is an intermediate transfer type color image forming apparatus utilizing an electrophotographic process technology. That is, the image forming apparatus 2 forms an image by: primarily transferring, to an intermediate transfer belt 421, toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) formed on respective photosensitive drums 413 (primary transfer); superimposing the four-color toner images on the intermediate transfer belt 421; and then secondarily transferring the superimposed toner images onto a sheet S sent out from one of sheet feeding tray units 51 a to 51 c of a sheet feeder 51.

Additionally, the image forming apparatus 2 adopts a tandem system whereby photosensitive drums 413 corresponding to the four colors of Y, M, C, and K are arranged in series in a travel direction of the intermediate transfer belt 421, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 421 by a single procedure.

As illustrated in FIG. 2, the image forming apparatus 2 includes an image reader 10, an operation display 20, an image processor 30, an image former 40, a sheet conveyer 50, a fixing device 60, and the controller 100.

The controller 100 includes a central processing unit (CPU) 101, a read only memory (ROM) 102, a random access memory (RAM) 103, and the like. The CPU 101 reads a program corresponding to processing content from the ROM 102, develops the program in the RAM 103, and performs centralized control for operation of the respective blocks in the image forming apparatus 2 in cooperation with the developed program. At this point, various kinds of data stored in a storage 72 are referred to. The storage 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) and a hard disk drive.

The controller 100 exchanges various kinds of data with an external device (such as a personal computer) connected to a communication network such as a local area network (LAN) or a wide area network (WAN) via a communication unit 71. The controller 100 receives, for example, image data (input image data) transmitted from the external device, and forms an image on a sheet S on the basis of the image data. The communication unit 71 includes a communication control card such as a LAN card.

As illustrated in FIG. 1, the image reader 10 includes: an automatic document feeding device 11 called an auto document feeder (ADF); and a document image scanner 12 (scanner).

The automatic document feeding device 11 conveys a document D placed on a document tray by a conveying device and sends the document to the document image scanner 12. Using the automatic document feeding device 11, it is possible to continuously and collectively read images of a large number of documents D placed on the document tray (including both faces).

The document image scanner 12 optically scans the document conveyed from the automatic document feeding device 11 onto a contact glass or a document placed on the contact glass, and reads a document image by forming, on a light receiving surface of a charge coupled device (CCD) sensor 12 a, an image of reflection light emitted from the document. The image reader 10 generates input image data on the basis of a reading result by the document image scanner 12. The input image data is subjected to predetermined image processing in the image processor 30.

As illustrated in FIG. 2, the operation display 20 includes, for example, a liquid crystal display (LCD) attached with a touch panel, and functions as a display 21 and an operating unit 22. The display 21 displays various kinds of operation screens, a state of an image, operating situations of the respective functions, and the like in accordance with display control signals received from the controller 100. The operating unit 22 includes various kinds of operation keys such as a numeric keypad and a start key, accepts various kinds of input operation by a user, and outputs an operation signal to the controller 100.

The image processor 30 includes a circuit and the like that applies digital image processing to input image data in accordance with initial settings or user settings. For example, the image processor 30 applies tone correction on the basis of tone correction data (a tone correction table) under the control of the controller 100. Furthermore, the image processor 30 applies, to the input image data, not only the tone correction but also various kinds of correction processing such as color correction and shading correction, compression processing, and the like. The image former 40 is controlled on the basis of image data applied with the above-described processing.

As illustrated in FIG. 1, the image former 40 includes: image forming units 41Y, 41M, 41C, and 41K to form images with the respective color toner of Y, M, C, and K components on the basis of the input image data; an intermediate transfer unit 42; and the like.

Each of the image forming units 41Y, 41M, 41C, and 41K for the Y, M, C, and K components has the similar configuration. For convenience of illustration and description, common constituent elements are denoted by the same reference signs, and in a case of distinguishing each of the constituent elements by colors, each reference sign is suffixed by Y, M, C, or K. In FIG. 1, only the constituent elements of the image forming unit 41Y for the Y component are denoted by reference signs, and the reference signs of the constituent elements of the other image forming units 41M, 41C, 41K are omitted.

Each image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, and a drum cleaning device 415.

The photosensitive drum 413 includes, for example, an organic photoreceptor in which a photoconductive layer made of a resin containing an organic photoconductor is formed on an outer peripheral surface of a drum-shaped metal base.

The controller 100 controls drive current supplied to a drive motor (not illustrated) that rotates the photosensitive drum 413, thereby rotating the photosensitive drum 413 at a constant circumferential velocity.

The charging device 414 is, for example, an electric charger, and uniformly charges, by generating corona discharge, a surface of the photosensitive drum 413 having photoconductivity to a negative polarity.

The exposure device 411 includes, for example, a semiconductor laser and irradiates the photosensitive drum 413 with laser light corresponding to an image of each color component. As a result, an electrostatic latent image of each color component is formed, due to a potential difference from a background region, in an image region included in the surface of each photosensitive drum 413 and irradiated with the laser light.

The developing device 412 is a developing device adopting a two-component inverting method, and forms a toner image by visualizing an electrostatic latent image by making developer of each color component adhere to the surface of the photosensitive drum 413.

The developing device 412 is applied with, for example, DC developing bias having the same polarity as a charge polarity of the charging device 414 or developing bias in which DC voltage having the same polarity as the charge polarity of the charging device 414 is superimposed on AC voltage. As a result, inversion development, in which the toner is made to adhere to the electrostatic latent image formed by the exposure device 411, is performed.

The drum cleaning device 415 is made to abut on the surface of the photosensitive drum 413, includes a plate-like drum cleaning blade or the like including an elastic body, and removes the toner not transferred to the intermediate transfer belt 421 and remaining on the surface of the photosensitive drum 413.

The intermediate transfer unit 42 includes the intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, and a belt cleaning device 426.

The intermediate transfer belt 421 includes an endless belt and is hung and stretched around the plurality of support rollers 423 like a loop. At least one of the plurality of support rollers 423 includes a drive roller, and other support rollers include driven rollers. For example, preferably, a roller 423A arranged more on a downstream side in a belt travel direction than a primary transfer roller 422 for the K component is a drive roller. With this configuration, it is easier to keep a constant travel speed of the belt at the primary transfer unit. When the drive roller 423A is rotated, the intermediate transfer belt 421 travels at the constant speed in a direction of an arrow A.

The intermediate transfer belt 421 is a belt having conductivity and elasticity, and includes a high resistance layer on a surface thereof. The intermediate transfer belt 421 is rotationally driven by a control signal from the controller 100.

The primary transfer roller 422 is arranged on an inner peripheral surface side of the intermediate transfer belt 421 in a manner facing the photosensitive drum 413 of each color component. When the primary transfer roller 422 is pressed against the photosensitive drum 413 while interposing the intermediate transfer belt 421, thereby forming a primary transfer nip in order to transfer a toner image from the photosensitive drum 413 to the intermediate transfer belt 421.

The secondary transfer roller 424 is arranged on an outer peripheral surface side of the intermediate transfer belt 421 in a manner facing a backup roller 423B arranged on a downstream side in the belt travel direction of the drive roller 423A. The secondary transfer roller 424 is pressed against the backup roller 423B while interposing the intermediate transfer belt 421, thereby forming a secondary transfer nip in order to transfer each toner image from the intermediate transfer belt 421 to a sheet S.

When the intermediate transfer belt 421 passes through each of the primary transfer nips, the toner image on each of the respective photosensitive drums 413 is sequentially superimposed and primarily transferred onto the intermediate transfer belt 421. Specifically, each of the toner images is electrostatically transferred to the intermediate transfer belt 421 by: applying primary transfer bias to each of the primary transfer rollers 422; and applying electric charge having an opposite polarity of the toner to a back-surface side of the intermediate transfer belt 421, that is to say, a side on which each of the primary transfer rollers 422 abuts.

After that, when the sheet S passes through the secondary transfer nip, the toner images on the intermediate transfer belt 421 are secondarily transferred to the sheet S. Specifically, the toner images are electrostatically transferred to the sheet S by: applying secondary transfer bias to the secondary transfer roller 424; and applying electric charge having an opposite polarity of the toner to a back-surface side of the sheet S, that is to say, a side on which the secondary transfer roller 424 abuts. The sheet S on which the toner images are transferred is conveyed toward the fixing device 60.

The belt cleaning device 426 removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer.

The fixing device 60 includes: an upper fixing unit 60A including a fixing surface side member arranged on a fixing surface of the sheet S, that is to say, on a surface side where the toner images are formed; a lower fixing unit 60B including a back-surface side support member arranged on a back surface of the sheet S, that is to say, an opposite surface side of the fixing surface; a heating source; and the like. The back-surface side support member is pressed against the fixing surface side member, thereby forming a fixing nip that nips and conveys the sheet S.

The fixing device 60 applies heating and pressurizing to the sheet S at the fixing nip, thereby fixing the toner images on the conveyed sheet S on which the toner images have been secondarily transferred. The fixing device 60 is arranged as a unit inside a fuser F.

The sheet conveyer 50 includes the sheet feeder 51, a sheet ejector 52, a conveyance path 53, and the like. Each of sheet S identified on the basis of a basis weight, a size, and the like is stored per preset sheet type (a standard sheet or a special sheet) in each of the three respective sheet feeding tray units 51 a to 51 c constituting the sheet feeder 51. The conveyance path 53 includes a plurality of pairs of conveyance rollers including a pair of registration rollers 53 a.

The sheets S stored in each of the sheet feeding tray units 51 a to 51 c are sent one by one to the image former 40 from an uppermost portion, and then conveyed via the conveyance path 53. In the image former 40, the toner images on the intermediate transfer belt 421 are collectively secondarily transferred to one surface side of the sheet S, and fixing processing is applied in the fixing device 60. The sheet S having the image formed thereon is ejected to the outside (the sheet stacking apparatus 3 in this example) by the sheet ejector 52 including sheet ejection rollers 52 a.

The sheet stacking apparatus 3 is an apparatus that continuously receives sheets S fed (ejected) from the apparatus on the upstream side (the image forming apparatus 2 in this example), stacks the received sheets S as a sheet bundle inside the apparatus main body, and takes out the stacked sheet bundle to the outside of the apparatus at appropriate time. The sheet stacking apparatus 3 is suitably used in a case of executing a print job of forming images on a large number of sheets S, for example, thousands of sheets by the image forming apparatus 2.

As illustrated in FIGS. 1 and 2, the sheet stacking apparatus 3 includes a stacking controller 300, a stacking conveyer 301, a shutter open level detector 302, a tray state detector 303, a first tray driver 304, a second tray driver 305, and the like. Furthermore, the sheet stacking apparatus 3 includes a shutter 330 on a front surface side of a substantially box-shaped housing (apparatus main body) thereof, and this shutter 330 can be moved up and down. Hereinafter, the term “apparatus main body” indicates the housing of the sheet stacking apparatus 3 unless otherwise particularly specified.

FIG. 3 is a diagram schematically illustrating a main part of the sheet stacking apparatus 3 from a left side, that is, from a downstream side in the sheet conveyance direction of FIG. 1. As illustrated in FIG. 3, the sheet stacking apparatus 3 includes a first stacking tray 310, a second stacking tray 320, a tray setting table 321, the shutter 330, a first switch 331, a second switch 332, a third switch 333, and the like. Additionally, although not illustrated, the sheet stacking apparatus 3 includes: a display that displays a state a the sheet stacking apparatus 3; an operation input device to be operated by a user; and the like.

Among the above, the first stacking tray 310, the second stacking tray 320, and the tray setting table 321 correspond to a “sheet stacker” of the present invention.

Additionally, the shutter 330 is a member that is opened/closed in a case of taking out sheets (a sheet bundle) stacked on the second stacking tray 320 or the like and in a case of returning the second stacking tray 320 or the like into the apparatus main body. The shutter 330 corresponds to an “openable member” of the present invention.

The stacking controller 300 of the sheet stacking apparatus 3 has a function of controlling the entire sheet stacking apparatus 3 while appropriately communicating with the controller 100 of the image forming apparatus 2. The stacking controller 300 of the sheet stacking apparatus 3 includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like. In the present embodiment, the stacking controller 300 corresponds to a “controller” of the present invention.

The CPU of the stacking controller 300 reads a program according to processing content from the ROM, develops the program in the RAM, and performs centralized control for operation of the respective blocks in the sheet stacking apparatus 3 in cooperation with the developed program. At this point, various kinds of data stored in a storage are referred to. The storage of the stacking controller 300 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) and a hard disk drive.

The stacking conveyer 301 has a function of conveying a sheet S ejected from the image forming apparatus 2 and stacking the conveyed sheet S on the first stacking tray 310. The stacking conveyer 301 corresponds to a “sheet conveyer” of the present invention.

The stacking conveyer 301 includes a conveyance roller (not illustrated) and a conveyance motor that drives the conveyance roller. The stacking controller 300 controls ON/OFF of rotation, a rotation speed, and the like of the conveyance roller, and thus, the stacking conveyer 301 conveys the sheet S ejected from the image forming apparatus 2 with the conveyance roller, and stacks the sheet S in the first stacking tray 310.

The first tray driver 304 includes: a drive source (hereinafter, referred to as a “first drive source” for convenience) such as a motor (not illustrated) to move the first stacking tray 310; a drive circuit; and the like. The first tray driver 304 corresponds to a “first mover” of the present invention.

That is, the first tray driver 304 drives the first drive source under the control of the stacking controller 300, thereby causing downward movement of the first stacking tray 310, that is, operation of moving the first stacking tray 310 toward the second stacking tray 320. Additionally, the first tray driver 304 drives the first drive source under the control of the stacking controller 300, thereby causing upward movement of the first stacking tray 310, that is, operation of separating the first stacking tray from the second stacking tray 320 to return the first stacking tray to an initial position. Furthermore, the first tray driver 304 drives the first drive source under the control of the stacking controller 300, thereby performing operation of adjusting a vertical position of the first stacking tray 310 so as to keep a constant upper end position of each stacked sheet S.

Moreover, the first tray driver 304 includes an actuator or the like (not illustrated) to move (retract) the first stacking tray 310 in a predetermined direction in order to deliver sheets (a sheet bundle) stacked on the first stacking tray 310 to the second stacking tray 320.

In the present embodiment, the first stacking tray 310 is movable in a vertical direction inside the apparatus main body of the sheet stacking apparatus 3. In one specific example, a guide rail (not illustrated) is provided inside the apparatus main body of the sheet stacking apparatus 3, and the first stacking tray 310 is moved in the vertical direction along the above-mentioned guide rail by transmitting power of the first drive source of the above-described first tray driver 304.

Note that an upper end detection sensor (not illustrated) that detects an upper end position of each of sheets S (a sheet bundle SS) stacked on the first stacking tray 310 and outputs a detection result thereof to the stacking controller 300 is provided inside the apparatus main body of the sheet stacking apparatus 3. Then, in the sheet stacking apparatus 3, the vertical position of the first stacking tray 310 is adjusted on the basis of the detection result of the upper end detection sensor.

That is, to stack the sheets S fed onto the first stacking tray 310 as much aligned as possible, it is required to keep, as constant as possible, the upper end position of the sheet bundle SS on the first stacking tray 310, that is, a position along a horizontal direction of an uppermost sheet S.

In contrast, in a case where the first stacking tray 310 is fixed inside the apparatus main body, the more the number of stacked sheets S is increased, the more the upper end position of the sheet bundle SS is raised, finally conveyance failure or jam of a sheet S may be caused. Therefore, in the sheet stacking apparatus 3, the position of the first stacking tray 310 is required to be lowered as the number of the stacked sheets S is increased.

Thus, in the sheet stacking apparatus 3, the first drive source of the first tray driver 304 is driven to adjust the vertical position of the first stacking tray 310 such that the upper end position of each of the sheets S (sheet bundle SS) detected by the upper end detection sensor is kept within a fixed range under the control of the stacking controller 300.

Additionally, the first stacking tray 310 is moved in a predetermined direction by, for example, actuating the actuator or the like of the above-described stacking conveyer 301, and delivers the stacked sheet bundle SS to the second stacking tray 320 (see, for example, FIG. 4B). In one specific example, the first stacking tray 310 includes a pair of members which face each other and stack the sheets S, and the stacked sheet bundle SS is delivered to the second stacking tray 320 by moving the pair of members in a manner respectively retracted to the downstream side and the upstream side in the conveyance direction of the sheets S.

The second tray driver 305 includes: a drive source (hereinafter, referred to as a “second drive source” for convenience) such as an actuator (not illustrated) to move, toward the outside of the sheet stacking apparatus 3, the tray setting table 321 on which the second stacking tray 320 is placed; a drive circuit; and the like. The second tray driver 305 corresponds to a “second mover” of the present invention.

The second stacking tray 320 and the tray setting table 321 are movable in a horizontal direction inside the apparatus main body of the sheet stacking apparatus 3. In one specific example, a guide rail (not illustrated) is provided inside the apparatus main body of the sheet stacking apparatus 3, and the tray setting table 321 is arranged in a manner movable in the horizontal direction (a lateral direction in FIG. 3) along the guide rail.

A size of the second stacking tray 320 in a plan view (a width in the conveyance direction and a depth direction) is larger than a maximum size of a sheet S stacked inside the sheet stacking apparatus 3. Also, the width in the conveyance direction of the tray setting table 321 in the plan view is slightly smaller than that of the second stacking tray 320.

On the other hand, the size in the depth direction of the tray setting table 321 in the plan view is larger than that of the second stacking tray 320. Specifically, as illustrated in FIG. 3, a deep end portion 321 a protrudes on a deep side of the tray setting table 321, and a front end portion 321 b protrudes on a front side of the tray setting table 321, respectively. Therefore, the size in the depth direction of the tray setting table 321 is larger by the sizes of the end portions 321 a and 321 b.

Here, the deep end portion 321 a of the tray setting table 321 has a height substantially same as that of a main body of the tray setting table 321, and is formed in a manner facing the first switch 331 described later (see FIG. 3). Additionally, even in a case where the tray setting table 321 is taken out from the sheet stacking apparatus 3 (apparatus main body) to the outside, the deep end portion 321 a remains in the apparatus main body (see FIG. 5B, for example).

On the other hand, as illustrated in FIG. 3, the front end portion 321 b of the tray setting table 321 has a height lower than those of the main body of the tray setting table 321 and the deep end portion 321 a.

The tray state detector 303 (see FIG. 2) has functions of: detecting whether or not the tray setting table 321 and the second stacking tray 320 are completely housed inside the apparatus main body; and outputting a detection result thereof to the stacking controller 300.

In the present embodiment, the tray state detector 303 has the first switch 331 (see FIG. 3) arranged on the deep side of the apparatus main body. In a case where the first switch 331 is pressed by the deep end portion 321 a of the tray setting table 321 and in a case where the first switch 331 is not pressed by the deep end portion 321 a, an ON/OFF state of the first switch 331 is switched. Then, the tray state detector 303 outputs the detected ON/OFF state of the first switch 331 to the stacking controller 300 as a detection signal.

The shutter 330 has a width longer than a width in the conveyance direction of the second stacking tray 320. Additionally, right and left end portions of the shutter 330 in FIG. 1 are installed in a manner each slidable along a recessed guide (not illustrated) that defines a substantially rectangular opening of the apparatus main body of the sheet stacking apparatus 3. Therefore, the shutter 330 can be moved in the vertical direction of the apparatus main body.

Thus, when the shutter 330 is moved (raised) up to a position where the open level becomes maximum, the shutter does not interfere with any one of: the tray setting table 321 and the second stacking tray 320 which are to be taken out to the outside later; and a sheet bundle SS (see FIG. 4B, for example) stacked on the second stacking tray 320 up to a maximum stacking height.

The shutter open level detector 302 has a function of detecting the open level (opened/closed state) of the shutter 330, and outputs a detection result thereof to the stacking controller 300. In the present embodiment, the shutter open level detector 302 includes the second switch 332 and the third switch 333 provided at the above-described guide of the apparatus main body. These configurations will be described in detail later.

Hereinafter, an outline of operation of the sheet stacking apparatus 3 will be described.

FIGS. 4A and 4B are diagrams illustrating operation of moving a sheet bundle SS stacked on the first stacking tray 310 to the second stacking tray 320 in the sheet stacking apparatus 3. Specifically, FIG. 4A illustrates a case where sheets S have been sequentially ejected from the sheet ejector 52 of the image forming apparatus 2 and a print job is completed in a state where the sheets S are stacked on the first stacking tray 310 as the sheet bundle SS. After that, the first drive source of the first tray driver 304 is driven under the control of the stacking controller 300, thereby moving the first stacking tray 310 toward the second stacking tray 320 as indicated by an arrow in FIG. 4A.

FIG. 4B illustrates a state after the sheet bundle SS on the first stacking tray 310 is moved to the second stacking tray 320. In this example, when the actuator or the like of the first tray driver 304 is driven under the control of the stacking controller 300, thereby moving the first stacking tray 310 so as to be separated to the upstream side and the downstream side in the conveyance direction. Thus, the sheet bundle SS on the first stacking tray 310 is moved to the second stacking tray 320.

FIGS. 5A and 5B are diagrams illustrating operation after moving the sheet bundle SS to the second stacking tray 320 in the sheet stacking apparatus 3.

As it can be grasped from a comparison between FIG. 4B and FIG. 5A, after the sheet bundle SS is moved to the second stacking tray 320, the shutter 330 is moved upward by, for example, manual operation (manual work) of a user and made into a fully-opened state. Subsequently, when the above-described second drive source is driven by the user pressing a switch (not illustrated), the tray setting table 321 and the second stacking tray 320 are taken out to the front side (right side in FIG. 5B) of the sheet stacking apparatus 3, and the sheet bundle SS on the second stacking tray 320 is exposed to the outside as illustrated in FIG. 5B.

After that, the shutter 330 is moved down in the sheet stacking apparatus 3 (see FIG. 6A), and the first drive source is driven under the control of the stacking controller 300, thereby moving up the first stacking tray 310 to the initial position (see FIG. 6B). At this time, the sheet stacking apparatus 3 becomes a state capable of newly stacking, on the first stacking tray 310, a sheet S ejected from the image forming apparatus 2.

On the other hand, the sheet bundle SS, which is exposed to the outside (on the front side) of the sheet stacking apparatus 3 while being stacked on the second stacking tray 320, is carried out at appropriate timing (see FIG. 7A). Here, FIG. 7A illustrates a case where only the sheet bundle SS is carried out while leaving the tray setting table 321 and the second stacking tray 320.

On the other hand, as a different conveying method, the second stacking tray 320 and the sheet bundle SS can be carried out together while leaving only the tray setting table 321. As another different conveying method, a base portion of a trolley (not illustrated) is inserted into the tray setting table 321, and a part of the tray setting table 321 (a top plate side), the second stacking tray 320, and the sheet bundle SS can be integrally placed on the trolley and carried out. Note that the above-described configurations and methods related to the conveyance of the sheet bundle SS are not directly related to a main part of the present invention, and therefore, illustration and detailed description thereof will be omitted.

Back to the description of the drawings, FIGS. 7B, 8A and 8B illustrate, in time series, an exemplary case of returning the tray setting table 321 and the second stacking tray 320 into the sheet stacking apparatus 3 after the sheet bundle SS is carried out by the various kinds of methods as described above.

That is, in the case of returning the tray setting table 321 and the second stacking tray 320 into the sheet stacking apparatus 3, the shutter 330 is moved up first to expose the opening on the lower side of the apparatus main body of the sheet stacking apparatus 3 as illustrated in FIG. 7B.

Subsequently, the tray setting table 321 and the second stacking tray 320 are moved (pushed inside by a user, for example) in a state where the opening is secured by keeping the shutter 330 on the upper side, and thus, the tray setting table 321 and the second stacking tray 320 are housed inside the apparatus main body (see FIG. 8A). Finally, the shutter 330 is moved down and thereby returned to a so-called initial state.

Thus, in the sheet stacking apparatus 3, the stacked sheet bundle SS is not directly carried out from the first stacking tray 310, but the sheet bundle SS stacked on the first stacking tray 310 is delivered to the second stacking tray 320 and the sheet bundle SS is carried out by pulling out the second stacking tray 320 to the outside of the apparatus.

According to the sheet stacking apparatus 3 having such a configuration, the work of carrying out the sheet bundle SS and the work of stacking the sheets S fed from the upstream device (the image forming apparatus 2 in this example) can be performed separately. Therefore, productivity is improved.

That is, in the sheet stacking apparatus 3, the first stacking tray 310 is returned to the initial position during a work process of carrying out the sheet bundle SS on the second stacking tray 320, and sheets S can be stacked again by promptly executing (or restarting) a next print job (or a print job stopped on the way due to a full load amount or the like).

More specifically, according to a configuration of a conventional sheet stacking apparatus, sheets S fed from an upstream image forming apparatus and a tray on which the sheets S are directly stacked are delivered to a trolley (carrier) all together, and then transported. Due to this, there is a problem that the sheet stacking apparatus cannot receive (stack) sheets until the sheets on the tray are removed and the tray is reset inside the apparatus main body.

Note that, for example, in a sheet stacking apparatus disclosed in JP 2008-94584 A, in a case of preliminarily preparing a plurality of trays that stacks sheets, the sheet stacking apparatus can continue receiving and stacking sheets by setting a different tray inside the apparatus at the time of transporting a current tray by the carrier as described above. However, in the case of preliminarily preparing the plurality of trays as described above, there is a problem in convenience because: the cost is increased by an amount corresponding to the number of trays; and a storage place for the trays is required to be secured.

In contrast, as described above, the sheet stacking apparatus 3 of the present embodiment includes: the first stacking tray 310 that stacks the sheets S and is moved up and down inside the apparatus main body; and the second stacking tray 320 that receives the sheets stacked on the first stacking tray 310 and can eject the received sheets to the outside of the apparatus while keeping the sheets are stacked thereon.

According to such a sheet stacking apparatus 3, sheet feeding to the sheet stacking apparatus 3 (sheet stacking processing) can be continued by moving up the first stacking tray 310 again (see FIG. 6B) while the second stacking tray 320 holding the large amount of sheets (the sheet bundle SS) received from the first stacking tray 310 is taken out from the sheet stacking apparatus 3 and transported.

By the way, the sheet stacking apparatus 3 having the above-described configuration has following technical problems.

For example, assume a state where a print job is completed, the first stacking tray 310 is returned to the initial position at the time of executing a next print job while the second stacking tray 320 having sheets S stacked is taken out and transported to a different place, and then a sheet S ejected from the image forming apparatus 2 is received.

After that, it is necessary to empty the second stacking tray 320 by moving, to some another place, the sheets stacked on the second stacking tray 320, and return the second stacking tray 320 into the sheet stacking apparatus 3 (see FIGS. 8A and 8B).

At this time, in the conventional general sheet stacking apparatus or the conventional general image forming system, printing operation of the image forming apparatus 2 is stopped (that is, the print job is interrupted) because a safety device is actuated on the basis of a detection result of a sensor or the like that detects an opened/closed state of the shutter 330. Accordingly, in the event of such stop or such interruption processing, there is a problem that the above-described advantage of the sheet stacking apparatus 3 of the present embodiment (productivity improvement by continuing sheet feeding) is eliminated.

To solve the above-described problem, for example, it is conceivable that the sensor or the like that detects the open/closed state of the shutter 330 is not provided so as to prevent the safety device from being actuated (prohibit actuation of the safety device) when the shutter 330 is opened.

However, such a configuration may have a problem that safety of a user who performs the work cannot be assured because the user can freely open and close the shutter 330 (that is, the safety device is not actuated) while the sheet stacking apparatus 3 is in service.

Specifically, in the case where the shutter 330 can be limitlessly opened and closed when a movable portion such as the first stacking tray 310 is moved down (see FIGS. 4A and 4B) or moved up (see FIGS. 6A and 6B), there is a possibility that a body (such as a hand or an arm) of an operator may be caught in the movable portion and get injured or the like.

Accordingly, in the sheet stacking apparatus 3, in a case where the opened/closed state of the shutter 330 is an intermediate state (see FIG. 7B, for example) between the fully-opened state (see FIG. 5A, for example) and a fully-closed state (see FIG. 3), the stacking conveyer 301 is controlled so as to convey the sheets S to the first stacking tray 310 (sheet stacker).

That is, when the print job is executed (at the time of execution or during execution thereof), in a case where the shutter 330 is in the fully-closed state, the stacking controller 300 controls the stacking conveyer 301 to convey the sheets S to the first stacking tray 310, whereas in a case where the shutter 330 is in the fully-opened state, the stacking controller 300 controls the stacking conveyer 301 so as not to convey the sheet S to the first stacking tray 310.

In contrast, in a case where the shutter 330 is in the intermediate state while the print job is executed (at the time of execution or during the execution thereof), the stacking controller 300 controls the stacking conveyer 301 so as to convey the sheets S to the first stacking tray 310.

Here, the “intermediate state” in the opened/closed state of the shutter 330 includes an open level state at which the tray setting table 321 and the second stacking tray 320 can be inserted and taken out from the apparatus main body without interfering with the lower side of the shutter 330 (see FIGS. 7B and 8A).

With the above-described configuration, in the case where the shutter 330 is in the intermediate state, sheets S sent from the upstream side (the image forming apparatus 2) can be received and stacked inside the sheet stacking apparatus 3. Therefore, the second stacking tray 320 and the like can be inserted or taken out without, for example, waiting for printing or stopping (interrupting) the printing, and the productivity can be improved.

In the present embodiment, the shutter open level detector 302 that detects the opened/closed state of the shutter 330 is provided as a first detector in order to detect the open level states corresponding to the “fully-opened state”, the “intermediate state”, and the “fully-closed state” of the shutter 330 described above (see FIG. 2).

Here, as illustrated in FIG. 3, the shutter open level detector 302 includes: the second switch 332 as a fully-closed state detector that detects whether or not the opened/closed state of the shutter 330 is the fully-closed state; and the third switch 333 as a fully-opened state detector that detects whether or not the opened/closed state of the shutter 330 is the fully-opened state.

In the present embodiment, each of the second switch 332 and the third switch 333 is a mechanical switch in which the ON/OFF state is switched by contacting the shutter 330, and each of the switches is arranged in a predetermined region of the apparatus main body where an edge of the shutter 330 passes through. Additionally, the stacking controller 300 detects or monitors the ON/OFF states of these switches 332 and 333.

In one specific example, the second switch 332 is provided at a height position in the vicinity of an upper end of the shutter 330 in the fully-closed state (see FIG. 3), and in the case where the shutter 330 in the fully-closed state is moved upward, the shutter contacts the second switch 332 and the ON/OFF state thereof is switched. According to this configuration, the stacking controller 300 can recognize a fact that the opened/closed state of the shutter 330 is changed from the fully-closed state to the intermediate state by detecting timing when the ON/OFF state of the second switch 332 is switched.

Similarly, the third switch 333 is provided at a height position in the vicinity of the upper end of the shutter 330 in the intermediate state (see FIG. 3 as appropriate), and in the case where the shutter 330 in the intermediate state is moved upward, the ON/OFF state of the third switch 333 is switched by the shutter contacting the third switch 333. In this case, the stacking controller 300 can recognize a fact that the opened/closed state of the shutter 330 is changed from the intermediate state to the fully-opened state by detecting timing when the ON/OFF of the third switch 333 is switched.

Furthermore, the stacking controller 300 can discriminate or determine the opened/closed state of the shutter 330 (any one of the fully-closed state, the intermediate state, and the fully-opened state in this example) by detecting the respective ON/OFF states of the second switch 332 and the third switch 333.

In other words, in a case where the ON/OFF state of the second switch 332 (fully-closed state detector) indicates (that is, detects) that the opened/closed state of the shutter 330 is not the fully-closed state and in a case where the ON/OFF state of the third switch 333 (fully-opened state detector) indicates (detects) that the opened/closed state of the shutter 330 is not the fully-opened state, the stacking controller 300 determines that the opened/closed state of the shutter 330 is in the intermediate state.

Note that the respective height positions of the second switch 332 and the third switch 333 provided in the apparatus main body, in other words, a boundary position between the fully-closed state and the intermediate state and a boundary position between the intermediate state and the fully-opened state can be arbitrarily changed in accordance with convenience, safety, and the like of an operator.

However, note that, when the opened/closed state of the shutter 330 is in the intermediate state, in the case of selling the third switch 333 at such an excessively high position that a user (operator) can limitlessly access the inside of the sheet stacking apparatus 3 in service, there is a possibility that the body of the operator (especially, a hand that touches a tray and the like) may get injured depending on a service state of the sheet stacking apparatus 3.

Specifically, for example, when the first stacking tray 310 is moved down as illustrated in FIG. 4A, in a case where the user (operator) moves up the shutter 330 so as to set the shutter to the intermediate state and puts the hand into the apparatus main body, there is a possibility that the operator's hand may be sandwiched between the first stacking tray 310 and the second stacking tray 320 and get injured.

Considering the above, it is desirable that the third switch 333 be set at a height position where the ON/OFF state is switched in a state where the open level of the shutter 330 is in such an open level that allows the tray setting table 321 and the second stacking tray 320 to be inserted and taken out but does not allow the operator's hand to enter the inside of the apparatus main body (see FIG. 8A).

Furthermore, in the present embodiment, the tray state detector 303 is provided as a second detector that detects the position of the second stacking tray 320, and safety of an operator can be further ensured by utilizing a detection result of the tray state detector 303. In this case, in the case where the opened/closed state of the shutter 330 is the intermediate state, the stacking controller 300 determines whether or not to convey sheets S to the first stacking tray 310 in accordance with a detection result of the tray state detector 303 (second detector), and controls the stacking conveyer 301 in accordance with the determination result.

That is, in the case where the opened/closed state of the shutter 330 is the intermediate state, and in a case where the tray state detector 303 detects that the tray setting table 321 is not housed inside the apparatus main body, the stacking controller 300 determines that a process is currently in the conveying process of the sheet bundle SS (see FIG. 7B), and controls the stacking conveyer 301 so as to convey the sheets S to the first stacking tray 310.

On the other hand, in the case where the opened/closed state of the shutter 330 is the intermediate state, and in a case where the tray state detector 303 detects that the tray setting table 321 is housed inside the apparatus main body, the stacking controller 300 determines that a process is not currently in the conveying process of the sheet bundle SS (see FIG. 4A), and controls the stacking conveyer 301 so as not to convey the sheets S to the first stacking tray 310. With such control, the safety of the operator can be ensured even in the case where the third switch 333 is set at the high position as described above.

In the present embodiment, the first switch 331 is provided as the tray state detector 303 on a wall surface of the apparatus main body facing the tray setting table 321 as illustrated in FIG. 3. This first switch 331 is a mechanical switch, and for example, the first switch 331 is turned ON when pressed by the deep end portion 321 a of the tray setting table 321, and the first switch 331 is turned OFF when the pressing is released.

In this case, the stacking controller 300 can determine whether or not the tray setting table 321 and the second stacking tray 320 are completely housed inside the apparatus main body by detecting the ON/OFF state of the first switch 331.

In one specific example, in a case where the first switch 331 is in the ON state and each of the second switch 332 and the third switch 333 is in the OFF state, the stacking controller 300 determines that: the tray setting table 321 and the second stacking tray 320 are completely housed inside the apparatus main body; and the shutter 330 is in the fully-closed state as illustrated in FIG. 3. In this case, the stacking controller 300 accepts execution of a print job by the image forming apparatus 2, and controls the stacking conveyer 301 so as to convey sheets S to the first stacking tray 310.

Additionally, in a case where the first switch 331 is in the ON state and each of the second switch 332 and the third switch 333 is in the ON state, the stacking controller 300 determines that: the tray setting table 321 and the second stacking tray 320 are completely housed inside the apparatus main body; and the shutter 330 is in the fully-opened state as illustrated in FIG. 5A. In this case, the stacking controller 300 transmits, to the image forming apparatus 2, a notification of not accepting execution of a print job by the image forming apparatus 2, and controls the stacking conveyer 301 so as not to convey the sheet S to the first stacking tray 310.

Note that FIG. 5A illustrates the state after completion of the print job. But, in another case where the state of shutter 330 becomes the fully-opened state while the print job is executed as illustrated in FIG. 4A, for example, the states of the switches 331, 332, and 333 also become the same as above. Furthermore, as described above, in the case where the third switch is set at the high position and the shutter 330 becomes a half-opened state that is almost fully-opened, it is necessary to ensure the safety of the user although the third switch 333 is in the OFF state. In this case also, the stacking controller 300 transmits, to the image forming apparatus 2, a notification of not accepting execution of a print job by the image forming apparatus 2, and controls the stacking conveyer 301 so as not to convey the sheets S to the first stacking tray 310. Thus, so-called emergency stop processing (a function as the above-described safety device) is conducted.

Additionally, in a case where the first switch 331 is in the OFF state and each of the second switch 332 and the third switch 333 is in the ON state, the stacking controller 300 determines that: the tray setting table 321 and the second stacking tray 320 are not completely housed inside the apparatus main body; and the shutter 330 is in the fully-opened state as illustrated in FIG. 5B. In this case, the stacking controller 300 transmits, to the image forming apparatus 2, a notification of not accepting execution of a print job by the image forming apparatus 2, and controls the stacking conveyer 301 so as not to convey the sheet S to the first stacking tray 310.

Furthermore, in a case where the first switch 331 is in the OFF state, the second switch 332 is in the ON state, and the third switch 333 is in the OFF state, the stacking controller 300 determines that: the second stacking tray 320 and the tray setting table 321 excluding a part (the end portion 321 a) of the tray setting table 321 are taken out of the apparatus main body; and the shutter 330 is in the intermediate state as illustrated in FIG. 6A. In this case, the stacking controller 300 performs control so as to return the first stacking tray 310 to the initial position (see FIG. 6B), accepts execution of a print job by the image forming apparatus 2, and controls the stacking conveyer 301 so as to convey the sheets S to the first stacking tray 310.

Thus, according to the present embodiment, the sheets S ejected from the image forming apparatus 2 can be stored and stacked in the first stacking tray 310 during the work of conveying the sheet bundle SS to the outside of the apparatus main body, thereby improving the productivity.

Note that, in a case where the shutter 330 is opened to the fully-opened state due to erroneous work by a user during the above-described work of moving the sheet bundle SS, the ON/OFF states of the respective switches 331 to 333 become the same as described above with reference to FIG. 5B. Therefore, the stacking controller 300 transmits, to the image forming apparatus 2, a notification of not accepting execution of a print job by the image forming apparatus 2 (a notification commanding interruption of the print job), and controls the stacking conveyer 301 so as not to convey the sheet S to the first stacking tray 310. With this control, the sheet feeding to the first stacking tray 310 is stopped, and fluctuation of the height position of the first stacking tray 310 is stopped. Therefore, it is possible to reduce a risk of the operator putting a hand into the apparatus main body and getting injured or the like.

Also, in a case where the shutter 330 is once opened to the fully-opened state during the work of moving the sheet bundle SS but the shutter 330 is returned to the intermediate state afterward, the stacking controller 300 transmits a command to the image forming apparatus 2 so as to restart a print job, and controls the stacking conveyer 301 so as to convey the sheet S to the first stacking tray 310. With this control, sheets S are fed (ejected) again from the image forming apparatus 2 and can be stored and stacked on the first stacking tray 310, thereby improving the productivity.

After that, similar control is performed by the stacking controller 300 also during the work of returning the tray setting table 321 and the second stacking tray 320 into the apparatus main body as illustrated in FIGS. 8A and 8B.

Note that in a case where the shutter 330 is opened to the fully-opened state or the half-opened state while the first stacking tray 310 is moved down due to completion of a print job by the image forming apparatus 2 during the work of moving the sheet bundle SS or during the work of returning the tray setting table 321 and the like into the apparatus main body, the stacking controller 300 controls the stacking conveyer 301 so as to stop moving down the first stacking tray 310. With this control, it is possible to reduce risk of an operator putting a hand into the apparatus main body and getting injured or the like.

Thus, in the case where the opened/closed state of the shutter 330 is the fully-opened state, the sheet stacking apparatus 3 causes the stacking controller 300 to control the stacking conveyer 301 so as not to convey sheets S to the first stacking tray 310, whereas in the case where the opened/closed state of the shutter 330 is the fully-closed state or the intermediate state, the sheet stacking apparatus 3 causes the stacking controller 300 to control the stacking conveyer 301 so as to convey the sheets S to the first stacking tray 310 considering the position of the tray setting table 321 or the like.

According to the sheet stacking apparatus 3 and image forming system 1 of the present embodiment which perform the above-described control, the productivity can be improved while ensuring safety of an operator. That is, according to the present embodiment, it is possible to achieve both the improvement in the productivity and safety of an operator.

From another viewpoint, in the sheet stacking apparatus 3 and the image forming system 1 of the present embodiment, in a case where the opened/closed state of the shutter 330 is the intermediate state having an open level at which the safety of an operator can be protected, conveyance control is performed in a manner similar to that in the case where the shutter 330 is in the fully-closed state. Thus, the productivity can be improved.

From still another viewpoint, in the sheet stacking apparatus 3 and the image forming system 1 according to the present embodiment, a so-called safety device is actuated on the basis of a combination of the ON/OFF states of the switches 331 to 333. Thus, safety in operator's work can be enhanced with a simple configuration.

Note that, in the above-described embodiment, the mechanical switches (331 to 333) are used to form the tray state detector 303 and the shutter open level detector 302, respectively. As another example, an optical sensor may be used to form the tray state detector 303 or the shutter open level detector 302, for example.

However, note that, in the case of using the optical sensor, an error may be caused by erroneous detection or a software bug. In such a case, since it is difficult to find a cause of malfunction, it is preferable to use a mechanical switch in which an ON/OFF state can be switched by utilizing a mechanical motion as described above.

In the case of using a switch adopting a system in which the shutter open level detector 302 is energized mechanically, that is, by a mechanical motion, it is easy to find which one of switches is malfunctioning even in a case where the ON/OFF state is not switched regardless of the open level of the shutter 330, for example.

Thus, since the mechanical switches (331 to 333) are used to form the tray state detector 303 and the shutter open level detector 302 respectively, the stacking controller 300 can determine the state of the sheet stacking apparatus 3 with high accuracy on the basis of a combination of the ON/OFF states of the respective switches 331, 332, and 333.

Furthermore, the stacking controller 300 can control the stacking conveyer 301 (sheet conveyer) in accordance with a determination result on the state of the sheet stacking apparatus 3 based on the combination of the ON/OFF states of the respective switches 331, 332, and 333 such that sheets S ejected from the upstream apparatus on the first stacking tray 310 can be placed (stacked) at appropriate time.

Moreover, the stacking controller 300 can stack the sheets S on the first stacking tray 310 and further move up/down the first stacking tray 310 at appropriate time considering safety of an operator in accordance with a determination result on the state of the sheet stacking apparatus 3 based on the combination of the ON/OFF states of the respective switches 331, 332, and 333.

In the above-described embodiment, the description has been provided assuming the exemplary configuration in which the shutter 330 is opened/closed by manual operation (manual work) of a user on the apparatus main body of the sheet stacking apparatus 3. As another exemplary configuration, a drive source such as a solenoid (not illustrated) may also be connected to the shutter 330, and the shutter 330 may be automatically opened/closed by drive power of the drive source under the control of the stacking controller 300.

In the above-described embodiment, the image forming system in which the sheet stacking apparatus 3 is directly connected to the image forming apparatus 2 has been exemplified. On the other hand, needless to mention, the exemplary configuration of the image forming system can be changed in various ways.

As another specific example of the image forming system, various kinds of post-processing apparatuses (not illustrated) may be arranged between the image forming apparatus 2 and the sheet stacking apparatus 3, and the sheet stacking apparatus 3 and the image forming apparatus 2 may be indirectly connected. In this case, the stacking controller 300 of the sheet stacking apparatus 3 can additionally or alternatively transmit, to the post-processing apparatuses, a notification regarding whether or not to accept execution of a job of post-processing in association with the control of the stacking conveyer 301.

Alternatively, as another specific example, it may be possible to adopt a sheet processing system in which a post-processing apparatus that performs post-processing for a printed sheet is connected to the upstream side of the sheet stacking apparatus 3 without including the image forming apparatus 2. In this case, the stacking controller 300 of the sheet stacking apparatus 3 is just to transmit, to the post-processing apparatus, a notification regarding whether or not to accept execution of a job of the post-processing in association with the control of the stacking conveyer 301.

Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. That is, the present invention can be implemented by various forms without departing from the spirit or essential characteristics thereof. The scope of the present invention should be interpreted by terms of the appended claims. 

What is claimed is:
 1. A sheet stacking apparatus comprising: a sheet stacker capable of stacking a sheet; a sheet conveyer that conveys the sheet to the sheet stacker; an openable member that can be opened/closed at time of taking out the sheet stacked on the sheet stacker; and a hardware processor that controls the sheet conveyer so as to convey the sheet to the sheet stacker in a case where an opened/closed state of the openable member is an intermediate state between a fully-opened state and a fully-closed state.
 2. The sheet stacking apparatus according to claim 1, wherein in a case where that opened/closed state of the openable member is the fully-closed state, the hardware processor controls the sheet conveyer to convey the sheet to the sheet stacker, whereas in a case where the opened/closed state of the openable member is the fully-opened state, the hardware processor controls the sheet conveyer so as not to convey the sheet to the sheet stacker.
 3. The sheet stacking apparatus according to claim 1, wherein the sheet stacker includes: a first stacking tray capable of stacking the sheet conveyed from the sheet conveyer; and a second stacking tray that receives the sheet stacked on the first stacking tray and is taken out of the sheet stacking apparatus in a state where the sheet is stacked on the second stacking tray, and further provided are: a first mover that moves the first stacking tray toward the second stacking tray; and a second mover that moves the second stacking tray to the outside of the sheet stacking apparatus.
 4. The sheet stacking apparatus according to claim 3, further comprising a first detector that detects an opened/closed state of the openable member.
 5. The sheet stacking apparatus according to claim 4, wherein the first detector includes: a fully-closed state detector that detects whether or not the opened/closed state of the openable member is the fully-closed state; and a fully-opened state detector that detects whether or not the opened/closed state of the openable member is the fully-opened state, and in a case where the fully-closed state detector detects that the opened/closed state of the openable member is not the fully-closed state and in a case where the fully-opened state detector detects that the opened/closed state of the openable member is not the fully-opened state, the hardware processor determines that the opened/closed state of the openable member is the intermediate state.
 6. The sheet stacking apparatus according to claim 5, further comprising a second detector that detects a position of the second stacking tray, wherein in a case of determining that the opened/closed state of the openable member is the intermediate state, the hardware processor determines, in accordance with a detection result of the second detector, whether or not to convey the sheet to the sheet stacker.
 7. The sheet stacking apparatus according to claim 6, wherein the fully-closed state detector, the fully-opened state detector, and the second detector respectively include switches in each of which an ON/OFF state is switched in accordance with an opened/closed state of the openable member and a position of the second stacking tray.
 8. The sheet stacking apparatus according to claim 7, wherein the hardware processor controls the sheet conveyer on a basis of a combination of the ON/OFF states of the switches.
 9. The sheet stacking apparatus according to claim 7, wherein the switches are mechanical switches in each of which the ON/OFF state is switched by a mechanical motion.
 10. An image forming system comprising: an image forming apparatus that forms an image on a sheet; and the sheet stacking apparatus according to claim 1, which stacks the sheet on which the image is formed by the image forming apparatus.
 11. A conveyance control method comprising: conveying a sheet to a sheet stacker capable of stacking a sheet; and performing control to convey the sheet to the sheet stacker in a case where an opened/closed state of an openable member is an intermediate state between a fully-opened state and a fully-closed state at time of taking out the sheet stacked on the sheet stacker. 